Moisture and density detector (MDD)

ABSTRACT

A Moisture and Density Detector (MDD) provides a method and apparatus to determine the moisture content and/or density, as well as presence and location of anomalies, and/or wood type of any dielectric material for various purposes. This device is very useful in detecting the moisture content of wood and wood-based materials, such as that of lumber in a dry kiln prior to, during and/or following drying. The MDD passes a radio frequency signal and/or any other signal between opposed or adjacent capacitance electrodes and measures the signal strength and phase shift of the signal. The addition of phase shift and multiple frequencies improves the accuracy of the results.

This application is a continuation-in-part of U.S. application Ser. No.10/061,374 filed Feb. 4, 2002, now allowed. The entirety of thatapplication is incorporated herein by reference.

FEDERALLY SPONSORED DEVELOPMENT

This invention was made with U.S. Government support under grant number2002-34158-11926 awarded by the Department of Agriculture. The U.S.Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention, the Moisture and Density Detector (MDD), relatesto an apparatus and method for detecting the moisture content and/ordensity of dielectric materials.

2. Related Art

Moisture Estimation Using Radio Frequency Signals

Several devices have been developed to measure moisture in materials.These devices are based primarily on resistance and capacitanceprinciples. Resistance is the opposition of a body or substance to acurrent passing through it. Capacitance is the property of a circuitelement that permits it to store charge. For resistance devices, adirect current (DC) radio frequency signal is passed through adielectric material (a material that does not conduct electricity) andthe signal strength is measured as a function of the resistance of thematerial. This resistance measurement is then converted to a moisturecontent value using correction factors for temperature and species.Capacitance devices measure capacitance value or “power-loss” andestimate moisture content based on known correlation.

U.S. Pat. No. 4,259,633 to Rosenau describes a resistance moisturecontent estimation technique. The technique applied by Rosenau andothers is limited in that it requires that metal pins be inserted intothe wood sample being tested. In addition, the electrolytic polarizationeffects when using DC voltage can result in measurement error.Inserted-pin resistance devices are considered to provide inaccurateestimates when the wood moisture content is above the fiber saturationpoint of 24 to 30 percent.

U.S. Pat. No. 3,600,676 to Lugwig et al. teaches the capacitancetechnique whereby an alternating current (AC) radio frequencycapacitance device was developed using adjacent electrodes and resonanceto determine the moisture content of bulk materials (i.e., coal, chips,etc.). This device applies a range of frequencies to the dielectricmaterial adjacent to the electrodes. The frequency with maximum signalstrength is termed the resonant frequency and is a direct function ofthe moisture content of the dielectric material. The Lugwig et al.device determines the resonant frequency at which signal strength(amplitude) reaches a maximum. Applicant's invention also applies arange of frequencies to the dielectric material and measures the signalstrength of each in terms of amplitude. However, Applicant's inventiondoes not determine the resonant frequency but rather relates themeasured amplitude of each frequency to predetermined values todetermine the moisture content of the dielectric material. In addition,in contrast to Applicant's invention, the Lugwig et al. device does notuse phase shift as additional information to estimate moisture contentor density.

U.S. Pat. No. 4,616,425 to Burns describes an opposed electrode devicebased on resistance or capacitance controlled oscillator circuits.Whether based on resistance or capacitance, this device requiresconversion to a frequency-dependent DC voltage. Signal strength of theDC voltage is related to predetermined voltage values for the dielectricmaterial to allow moisture content estimation. Direct contact with thedielectric material is required. In contrast to Burns, Applicant'sinvention does not employ conversion from AC signal to DC signal. Inaddition, direct physical contact with the wood surface is possible, butnot necessary. Furthermore, Burns does not use measurement of phaseshift to improve the moisture content estimate. The Burns device alsohas no capability to estimate dielectric material density.

U.S. Pat. No. 3,430,357 to Perry discloses an opposed electrode devicethat measures capacitive impedance and associated moisture content in astack of lumber in a dry kiln. The resistance between a capacitanceprobe inserted several courses of lumber above a ground electrode givesa measure of stack moisture content in the lumber between theelectrodes. This method requires direct contact between the capacitanceprobe and the lumber. With the Perry device, an AC signal is convertedto a DC signal prior to measurement of the signal strength as voltage.Perry differs from Applicant's invention in that Applicant directlymeasures the strength of the AC signal. Perry also does not employ aphase shift measurement to improve the moisture content estimate. Inaddition, the Perry device has no capability to estimate dielectricmaterial density.

U.S. Pat. No. 4,580,233 to Parker et al. teaches an adjacent electrodeAC moisture sensing device with two alternating frequencies thatmeasures the imbalance in a capacitance bridge to estimate the moisturecontent of dielectric materials. Circuitry and methodology isincorporated to correct for potential wood temperature differences. Aswith the Lugwig et al., Burns, and Perry disclosures, the AC signal isconverted to a DC signal prior to measurement of voltage to determinesignal strength. This differs from Applicant's invention, which directlymeasures the strength of the AC signal. In addition, Parker et al. doesnot employ phase shift either to improve the moisture content estimateor to allow for estimation of dielectric material density.

U.S. Pat. No. 5,402,076 to Havener et al. recites a portable device,similar to Perry's device, that measures moisture content in a stack oflumber but with the AC radio frequency signal transmitted betweenadjacent electrodes. As with Perry, Applicant's invention differsbecause Applicant measures the phase shift and has the capability toestimate wood density.

U.S. Pat. No. 5,486,815 to Wagner discloses an in-line AC moisture meteremploying opposed capacitance electrodes to sense moisture content inlumber moving between the electrodes. A single 4 MHz frequency istransmitted between electrodes and the received signal strength ismeasured to provide an estimate of the wood moisture content. The 4 MHzsignal is applied to two pairs of electrodes with a 20-volt peak-to-peakamplitude signal applied to one pair and a 4.5 volt peak-to-peakamplitude signed to the other. The 4.5 volt signal is applied 180°out-of-phase with the higher 20-volt signal. Wagner teaches thatanalysis of the out-of-phase signal responses reduces the effects on thesignal of electrical loading of the material. Wagner differs fromApplicant's invention because Wagner does not improve the estimate ofmoisture content by adding phase shift information and Wagner has nodescribed capability to estimate the dielectric material density. Thisdevice is also limited to detection of moisture content below 24percent.

The teachings described above have employed measures of signal strengthof both resistance and capacitance electrodes to estimate dielectricmaterial moisture content. Both AC and DC devices have been developed.However, none of the described devices are reportedly accurate inmeasuring moisture content above the fiber saturation point ofapproximately 24 to 30 percent moisture content. In addition, none haveemployed measurement of signal phase shift to improve their estimate ofmoisture content. Furthermore, none report the capability of estimatingthe density of the dielectric material by combined analysis of amplitudeand phase shift of a radio frequency signal.

U.S. Pat. No. 5,086,279 to Wochnowski discloses a means for estimatingmoisture content in a stream of materials by both reflecting and passingelectrical energy through the stream in the form of infrared, microwave,or energy generated by a high-frequency oscillator circuit. For each ofthe electrical energy types, the energy is both reflected from andtransmitted through the material stream. The transmitted energy from thehigh-frequency oscillator may be inferred to be in the same radiofrequency range as Applicant's invention, although Wochnowski did notdefine the spectrum.

The Wochnowski moisture content estimate of the stream of materialsdepends on measures of signal strength and phase shift with eachobtained by two methods. The two methods are to obtain a reflectedsignal detected by a sensor on the same side of the stream of materialsand also a through signal such as is obtained by an opposed or adjacentelectrode configuration. Therefore, the moisture content estimateprovided by Wochnowski depends partially on the correction for the massof the stream of materials by analysis of the “damping of oscillations”of electromagnetic waves through a first signal and a second (reflected)signal. Likewise, additional information for the moisture contentanalysis is obtained from the phase shift of both a through andreflected signal.

Applicant's invention differs from Wochnowski in that it requires noinformation on reflected energy but depends solely on its estimate ofmoisture content and density based on passage of the signal between theelectrodes. In addition, Applicant compares phase shift and signalstrength changes, caused by interaction of the radio frequency signalwith the dielectric material, to predetermined values to provide theestimation of moisture content and density. Wochnowski describes nomethod for comparing predetermined values to correlate measured phaseshift and signal strength decrease to expected values for the dielectricmaterial at given moisture content's and densities. Applicant alsoprovides an estimate of dielectric material density that the Wochnowskidevice does not provide.

In a 1993 writing, Torgovnikov discloses dielectric constants, measuresof signal strength, and loss tangent values for radio frequencies from20 to 1000 Hz. G. Torgovnikov, DIELECTRIC PROPERTIES OF WOOD ANDWOOD-BASED MATERIALS 174-181 (1993). (The terms loss tangent and phaseshift are both referenced herein. While these terms differ in theirmeaning, they are mutually direct functions with one easily derived fromthe other. For this reason, devices designed to provide information forone also indirectly provide the other value. In that sense these termswill be used interchangeably.) For all frequencies tested, Torgovnikovshows via plotted regressions that the rate of increase in thedielectric constant is higher for moisture content below the fibersaturation point. The plotted slopes of the regression lines also appearto have significant slope above the fiber saturation point. Theseplotted regression lines, however, represent the mean dielectricresponse for a range of wood specific gravity values.

Torgovnikov also teaches that the dielectric response is stronglyinfluenced by the wood specific gravity. Therefore, dielectric constantinformation alone will not allow an accurate estimation of wood moisturecontent because of the confounding influence of wood density. Withcurrent methods this confounding influence can only be eliminated if asingle wood density is scanned or if the density of specimens is known.Torgovnikov does not provides a method to improve moisture contentestimate by including phase shift or loss tangent as a predictivevariable.

Moisture Estimation Using Microwaves

Attempts have been made to measure the moisture content of materialsusing microwave energy. U.S. Pat. Nos. 4,727,311 and 5,767,685 to Walkerteach ways to measure the moisture content of materials such as sand andcoal. In these cases, two microwave frequencies are passed through amaterial in order to determine moisture content. The difference betweenthe two signals assists in determining moisture content.

U.S. Pat. No. 4,674,325 to Kiyobe et al. calculates moisture content bypassing material between non-contacting microwave horns. The basisweight is detected with an ionizing chamber.

U.S. Pat. No. 5,315,258 to Jakkula et al. discloses a radar systemdeveloped for measuring the moisture content of materials. There, thechange in velocity of the microwaves within the material is correlatedto differences in moisture content.

The Walker, Kiyobe et al., and Jakkula et al. teachings differ fromApplicant's invention in that a microwave signal rather than signals inthe radio frequency spectrum are utilized. Microwave devices requirewave guides to transmit and receive the signals while radio frequencydevices such as the Applicant's require only electrodes. These microwavedevices described also do not have the capability to estimate dielectricmaterial density.

The following disclosures describe microwave devices based on theattenuation of the microwave signal to estimate moisture contentcombined with information on phase shift of the microwave signal toprovide wood density information:

-   -   R. King et al., Microwave Measurement of the Complex Dielectric        Tensor of Anisotropic Slab Materials, in PROCEEDINGS OF A        TECHNOLOGY AWARENESS SEMINAR (Nov. 15-16, 1987).    -   R. King et al., Measurement of Basis Weight and Moisture Content        of Composite Boards Using Microwaves, in PROCEEDINGS OF THE 8TH        SYMPOSIUM ON THE NONDESTRUCTIVE TESTING OF WOOD (Sep. 23-25,        1991).    -   P. Martin et al., Evaluation of Wood Characteristics: Internal        Scanning of the Material by Microwaves, in 21 WOOD SCIENCE TECH.        367-371 (1987).    -   P. Martin et al., Industrial Microwave Sensors for Evaluation of        Wood Quality, in FOURTH INT'L CONFERENCE ON SCANNING TECHNOLOGY        IN THE WOOD INDUSTRY (1991).    -   J. Portala & J. Ciccotelli, Nondestructive Testing Techniques        Applied to Wood Scanning, in 2 INDUSTRIAL METROLOGY 299-307        (1992).

King et al. (1987), King et al. (1983), Martin et al. (1987), Martin etal. (1991), and Portala et al. (1992) depend for their estimates ofmoisture content and density on the analysis of both attenuation andphase shift. These devices differ from applicant's device in that themicrowaves are applied by horns, rather than by the electrodes utilizedby Applicant's device. No electrode based radio frequency or microwavedevice has been disclosed that combines analysis of changes in signalamplitude and phase shift to estimate wood moisture content and density,with the exception of Wochnowski. As discussed, this device requiresinformation on both reflected and through-material amplitude and phaseshift signals to obtain estimated material moisture content.

Radio Frequency Moisture Gradient Estimation

An impedance detector disclosed by Tiitta et al. measures the moisturegradient in wood. M. Tiitta et al., Development of an ElectricalImpedance Spectrometer for the Analysis of Wood Transverse MoistureGradient, in PROCEEDINGS OF THE 12^(TH) INT'L SYMPOSIUM ONNONDESTRUCTIVE TESTING OF WOOD (Sep. 13-15, 2000). Electrodes containedin a probe are placed on the wood surface. One electrode transmits anelectrical signal at frequencies below 5 MHz, and the second receivesthe signal. A variable electric field is developed between theelectrodes. Analysis of the behavior of impedance, or signal strength,for the various frequencies transmitted through the wood allowsestimation of the moisture gradient within the wood. This device wasdeveloped to sense the moisture gradient in logs.

Writings by Sobue and Jazayeri et al. have demonstrated a method tosense the moisture gradient in wood by what Sobue termed ElectrodeScanning Moisture Analysis (ESMA). N. Sobue, Measurement of MoistureGradient in Wood by Electrode Scanning Moisture Analysis ESMA, inPROCEEDINGS OF THE 12^(TH) INT'L SYMPOSIUM ON NONDESTRUCTIVE TESTING OFWOOD (Sep. 13-15, 2000); S. Jazayeri & K. Ahmet, Detection of TransverseMoisture Gradients in Timber by Measurements of Capacitance Using aMultiple-Electrode Arrangement, 50 FOREST PROD. J. 27-32 (2000). ESMAdetermines moisture content at various depths through wood thickness bymanipulating the distance between adjacent electrodes on a single woodsurface between 0.43 in. (11 mm) and 1.97 in (50 mm), shown in FIG. 1.Examination of the capacitance changes developed by manipulation ofelectrode distance allows computation of wood moisture gradient atvarious depths through wood thickness. Sobue's method allowedmeasurement of moisture content in wood up to 120 percent. Sobue andJazayeri et al., however, demonstrated that this method would work foronly a single wood density in which moisture content levels weremanipulated.

The Tiitta et al., Sobue, and Jazayeri et al. devices are adjacentelectrode impedance devices that are designed to estimate moisturegradient rather than average moisture content. The ability to estimatewood density as well as moisture gradient was not demonstrated by thisdevice. By contrast, Applicant's invention is an opposed or adjacentplate capacitance device that senses mean moisture content and may alsoprovide an estimate of wood density. Neither the Tiitta et al., Sobue,or Jazayeri et al. devices employ phase shift to improve their estimateof moisture content or to provide an estimate of wood density.

U.S. Pat. No. 5,585,732 to Steele et al. and two writings by Steele etal. have disclosed a method for detecting density differences in scannedlumber by a radio frequency method with opposed electrodes. P. Steele &J. Cooper, Estimating Strength Properties of Lumber with Radio FrequencyScanning, in PROC. OF THE 4TH INT'L CONFERENCE ON IMAGE PROCESSING ANDSCANNING OF WOOD (Aug. 21-23, 2000); P. Steele et al., Differentiationof Knots, Distorted Grain, and Clear Wood by Radio-Frequency Scanning,50 FOREST PROD. J. 58-62 (2000). To date, only detection of knots andvoids has been described as being detected. The application of phaseshift or loss tangent to assist in more accurately estimating dielectricmaterial moisture content or estimating density has not been disclosedfor this or any other radio frequency device.

The disclosures by Steele et al. employed dielectric properties and wooddensity in the estimation of wood strength by radio frequencycapacitance employing a variation of the Steele et al. device. However,the Steele et al. method depended on prior knowledge of wood moisturecontent with statistical correction for the known moisture contentdifferences. Validation of this method showed an R² value of 0.67between attenuated dielectric signal and lumber modulus of rupture. Onlya single radio frequency signal attenuation measurement to providespecific gravity estimates was employed. Applicant's invention, bycontrast, may employ single or multiple radio frequency signals toobtain dielectric constant. The Steele et al. method did not measurephase shift to improve the estimate of wood density.

Wood Strength Estimation Based On Density Detection

The amount of lumber graded by machine stress rating (MSR) has continuedto increase since the development of the technology in the early 1960's.This growth has been driven by the significant premium in value for MSRversus visually graded lumber in certain lumber grades. MSR gradedlumber is mechanically flexed to obtain a flatwise modulus ofelasticity. In a 1968 writing, Muller teaches a method of estimatinglumber grade based on the known relationship between modulus ofelasticity and modulus of rupture combined with additional informationfrom visual inspection of the lumber. P. Muller, MechanicalStress-Grading of Structural Timber in Europe, North America andAustralia, 2 WOOD SCI. & TECH. 43-72 (1968). In addition, in 1997Biernacki et al. indicated a significant potential for increased lumbervalue from improved accuracy in lumber grading. R² values based onrelating modulus of elasticity to modulus of rupture are speciesdependent but are approximately 0.50. J. Biernacki et al., EconomicFeasibility of Improved Strength and Stiffness Prediction of MEL and MSRLumber, 47 FOREST PROD. J. 85-91 (1997).

U.S. Pat. No. 4,941,357 to Schajer discloses an alternative to MSRlumber grading that is a system that estimates lumber strength based onx-ray through-lumber-thickness scanning. By this method the lumberstrength is estimated by assigning a clear wood strength value withdeductions based on knot presence indicated by specific gravity scans.Lumber strength estimations based on x-ray scanning is reported to behigher than MSR estimates with R² values ranging between 0.68 and 0.78for southern yellow pine lumber.

Applicant's invention has potential as an MSR device capable ofpredicting clear wood density. In such use, Applicant's invention willrequire a knot detection system such as a digital camera, ultrasound,radio frequency, infrared, etc. MSR lumber grading requires informationon knot size and location in addition to density of clear wood. Alsorequired will be techniques and software to correct for knot influenceon lumber strength.

Additional Information

Researchers have employed microwave horns and open-ended coaxial cablesto detect the moisture content, density, and characteristics ofbiological tissue including wood. Some devices such as Walker (U.S. Pat.Nos. 4,727,311 and 5,767,685), Kiyobe et al. (U.S. Pat. No. 4,674,325)utilize horns to direct microwaves through material and determine themoisture content based on the microwave attenuation. Jakkula et al.(U.S. Pat. No. 4,674,325) disclose a radar system that passes microwavesthrough materials whereby moisture content is correlated to changes inmicrowave velocity. Applicant's invention, by contrast, utilizesmicrowave signals applied by electrodes rather than horns. Also, inaddition to signal attenuation, phase shift information is utilized byApplicant to allow more accurate estimation of dielectric materialmoisture content and density.

Other researchers, listed below, have applied microwaves to wood withmicrowave horns. They have measured both the attenuation and phase shiftof the microwave signal and have utilized the known relationship ofthese signals to estimate both wood density and moisture content.Applicant's invention is similar to these devices and methods describedin that the combined information on signal attenuation and phase shiftis utilized to estimate wood moisture content and density. However,Applicant's device employs electrodes rather than horns to apply andreceive the microwaves.

-   -   R. King et al., Microwave Measurement of the Complex Dielectric        Tensor of Anisotropic Slab Materials, in PROCEEDINGS OF A        TECHNOLOGY AWARENESS SEMINAR (Nov. 15-16, 1987).    -   R. King et al., Measurement of Basis Weight and Moisture Content        of Composite Boards Using Microwaves, in PROCEEDINGS OF THE 8TH        SYMPOSIUM ON THE NONDESTRUCTIVE TESTING OF WOOD (Sep. 23-25,        1991).    -   P. Martin et al., Evaluation of Wood Characteristics: Internal        Scanning of the Material by Microwaves, in 21 WOOD SCIENCE TECH.        367-371 (1987).    -   P. Martin et al., Industrial Microwave Sensors for Evaluation of        Wood Quality, in FOURTH INT'L CONFERENCE ON SCANNING TECHNOLOGY        IN THE WOOD INDUSTRY (1991).    -   J. Portala & J. Ciccotelli, Nondestructive Testing Techniques        Applied to Wood Scanning, in 2 INDUSTRIAL METROLOGY 299-307        (1992).

Wochnowski (U.S. Pat. No. 5,086,279) has disclosed application ofelectromagnetic waves and simultaneous measurement of their transmissionthrough, and reflectance from, materials. He utilized this informationto estimate moisture content and density of the materials. Means ofapplication and frequency was not specified. Applicant's invention doesnot utilize electromagnetic wave reflectance information to arrive at anestimate of dielectric material moisture content and density.

Numerous researchers, such as those listed below, have employedopen-ended coaxial cables applying microwaves to measure dielectricproperties of biological materials, including wood. Applicant'sapplication of microwave signals is achieved with electrodes rather thanwith open-ended coaxial cables.

-   -   Atheny, T. W., M. A. Stuchly & S. S. Stuchly, 1982. Measurement        of RF Permittivity of Biological Tissues with an Open-Ended        Coaxial Line. IEEE. TRANS. MTT. 30:82-86.    -   Hagl, D. M., D. Popovic, S. C. Haguess, J. H. Brooke, & M.        Okoniewski. 2003. Sensing Volume of Open-Ended Coaxial Probes        for Dielectric Characterization of Breast Tissue at Microwave        Frequencies. IEEE. TRANS. MTT. 51(4):1194-1206.    -   Kabir, M. F., W. M. Daud, K. B. Khalid & H. A. A. Sidek. 2001.        Temperature Dependence of the Dielectric Properties of Rubber        Wood. WOOD AND FIBER SCIENCE. 33(2):233-238.

Steele & Kumar (U.S. Pat. No. 5,585,732) describe a radio frequency knotand void detection device utilizing opposed electrodes to detect knotsand voids.

Forrer & Funck have also utilized a variation of a device disclosed byIchijo in 1953. The Ichijo device is a resonant guard electrode designfor sensing dielectric properties of dielectric materials. Opposedelectrodes are placed in direct contact with surface of the dielectricmaterial. Forrer & Funck applied their variant of the device to detectwood types such as knots, clear wood, pitch streaks, pitch pockets,voids and blue stain. Moderate success in correlating these defect typeswith attenuation and phase shift were successful but considerableoverlap was found among these measures depending on the wood types.Frequency applied was in the radio frequency range between 1.4 and 20MHz and was, therefore, restricted to the radio frequency range. Thiswork by Forrer & Funck and by Ichijo was reported in the followingpapers:

-   -   Forrer, J. & J. Funck. 1998. Dielectric Properties of Defects on        Wood Surfaces. HOLZ ALS ROH-UND WERKSTOFF. 56(1):25-29.    -   Ichijo, B. 1953. On the New Method of Measuring Dielectric        Constant and Loss Angles of Semiconductors. J. APPL. PHYS.        24(3):307-311.

Applicant's invention differs from the Forrer & Funck device in severalimportant ways, including but not limited to the following. Oneimportant difference is that the Forrer & Funck device utilizes aresonance-based method and circuit to determine the dielectric constantand loss tangent of the wood types. The resonance device requiresrelatively complex circuitry comprising multiple resistors andcapacitors. Also, the dielectric material scanned must be physicallymanipulated multiple times following calibration steps to determine thedielectric constant and loss tangent of the dielectric material. Thismethod is obviously not suited to scanning wood to detect wood types forindustrial purposes. Applicant's invention, by contrast, applies adiscrete frequency and utilizes measurement devices to determineattenuation (related to dielectric constant) and phase shift (related toloss tangent). Thus, applicants method is adaptable to industrialscanning speeds.

Forrer & Funck also demonstrate no method for identifying wood typesfrom the dielectric constant and loss tangent data. Neither regressionequations nor threshold values based on predetermined values wereutilized. Rather, dielectric constant values were merely plotted versusloss tangent values to indicate a graphical relationship anddistribution of response to wood types. Thus, applicants method isadaptable to industrial scanning speeds.

Researchers, listed below, have reported on a method and device todetect knots and other anomalies in logs by analysis of depolarizedreflected microwaves transmitted from a microwave horn. Knots and logpith were successfully visualized. This device differs from Applicant'smethod in that microwaves are applied by Applicant by electrodes ratherthan horns.

-   -   Kaestner, A. P. and L. B. Baath. 2000. Microwave Polarimetry        Based Wood Scanning. PROC. OF THE 12th INT. SYMPOSIUM ON        NONDESTRUCTIVE TESTING OF WOOD. University of Western Hungary,        September 13-15. Sopron, Hungary. 474 p.

The patent titled “Determining the Dielectric Properties of Wood,”(DDPW), numbered PCT/US96/03604 with International Publication Number WO96/28741 and International Publication Date Sep. 19, 1996, invented byVenter & Viljoen, provides no method for determining the density of thewood between the electrodes.

The patent titled ”Dielectric Sensor Apparatus”, numbered U.S. Pat. No.5,654,643, invented by Bechtel et al. senses dielectric materialsutilizing cancellation of capacative coupling.

BACKGROUND OF THE TECHNOLOGY

After logs are milled and lumber is created, the lumber is usuallydried. Softwood lumber is a challenge to dry, and hardwood lumber iseven more difficult. A key difference between hardwood and softwoodlumber drying is the initial moisture content at the start of kilndrying. Wood moisture content may vary from 0% to a “green” measure. Agreen measure of moisture content may be as high or higher than 200percent. Softwood lumber is dried green immediately after it is sawn.The average initial moisture content of softwood lumber is often greaterthan one-hundred percent, based on oven-dry weight. Typically, hardwoodlumber has a significantly lower initial moisture content than softwoodlumber. When dried directly from the saw, hardwood lumber is typicallybetween sixty and eighty percent moisture content while softwood lumberfrequently exceeds 100 percent moisture content. Often, hardwood lumberis air dried to reduce its initial moisture content to approximately 25percent before being dried. In contrast, softwood lumber is often driedgreen at, or above, 100 percent moisture content.

Lumber in dry kilns can be monitored for drying rate and for finalmoisture content at the drying schedule endpoint by either moisturecontent schedules or time-based schedules. Moisture content schedulesmonitor the rate of drying by periodically weighing previously cut shortlumber samples during drying to measure the moisture content. Time-basedschedules do not require lumber samples, but instead assume that therate of drying is correlated with kiln conditions and the time overwhich the conditions are applied to the lumber. Time-based schedules arewidely used in the drying of softwood lumber because softwood lumber isless susceptible to drying degrade caused by drying the wood at animproper rate. However, failure to control the drying rate when applyingpre-set time schedules is responsible for considerable lumber degradeduring drying. In order for time-based schedules to work well, eachlumber load placed in the kiln must have approximately the same initialmoisture content, the same permeability, and kiln conditions must beidentical from charge to charge. These requirements are not alwayssatisfied and lumber drying degrade often occurs.

For most hardwood species, moisture content schedules must be used toprevent dramatic value losses from drying degrade. Traditional moisturecontent schedules require the kiln operator to control the drying rateby monitoring the moisture content of several kiln samples. Thesesamples are two to three-feet long and are dried with the kiln charge oflumber. Prior to the start of drying, a moisture content section is cutfrom each kiln sample. This section is rapidly oven dried to determinethe initial moisture content of the wood going into the kiln. Thisinitial moisture content value is used in conjunction with the sampleweight to determine the samples' moisture content throughout the dryingrun. This continual monitoring allows control of the kiln conditions,and the lumber's drying rate is based on the average sample moisturecontent.

The process of monitoring kiln samples requires kiln operators torepeatedly enter the dry kiln to remove kiln samples for monitoring byweighing. Following weighing, the kiln samples must be returnedimmediately to the dry kiln. Softwood lumber of nominal two-inchthickness is dried at high temperatures from green wood and the dryingprocess usually requires less than 24 hours. In the case of air-driedhardwoods of four-quarter-inch thickness, the approximate drying time isbetween four and eleven days.

Monitoring moisture content samples over a short-time interval (24 hoursor less) makes it difficult for operators to apply moisture contentschedules for softwoods without additional technology. For both hardwoodand softwood, kiln drying technological developments in recent yearshave produced several new methods to estimate the moisture contentdrying rate and drying end point. Reports on the effectiveness of thesesystems has been provided by Culpepper. L. Culpepper, HIGH TEMPERATUREDRYING 258-262 (1990).

One method for estimating the moisture content drying rate istemperature drop-across-the-load monitoring, which monitors thetemperature of the air flowing across the drying lumber. The airtemperature decrease from lumber entry to lumber exit is closelycorrelated to the wood moisture content for moisture content below thefiber saturation point, but the method is inaccurate above the fibersaturation point.

Another method for estimating the moisture content drying rate useselectrical resistance devices and employs pairs of pins inserted intoholes drilled into the lumber. The distance between the pins is limited(1″ to 2″) to allow an applied low voltage to flow between the two pins.The resulting resistance is measured and correlated to wood moisturecontent. The resistance devices accurately predict the moisture contentbelow the fiber saturation point, but inaccurately predict the woodmoisture content above the fiber saturation point.

An additional method uses an electrical capacitance method to measurethe capacitance between plates inserted in the stack and kiln railswhich are grounded. This method has been shown to provide a moisturecontent measurement that is often not accurate.

Weight-based systems are another method used to measure wood moisturecontent. These systems measure the total weight of kiln lumber duringdrying. This allows close monitoring of the drying rate. These systemsare reportedly accurate, but problems with sensor durability in theharsh kiln environment and the relatively high cost of usingweight-based systems has limited their widespread adoption.

A more recent weight-based system not reviewed by Culpepper monitors theweight of a kiln sample suspended in the kiln plenum, which is the spacearound the lumber. This system is reportedly effective but therelatively high cost of the system has limited its adoption.

As summarized above, systems that measure moisture content during kilndrying to monitor drying rate and drying end point are available.However, these systems are relatively expensive and not always effectiveat monitoring wood moisture content. There exists a need for improvedmethods to monitor drying rate and drying end point.

The ability to estimate wood density is also needed in the woodprocessing industry. The term density as employed herein refers to theoven-dry specific gravity of a dielectric material. A dielectricmaterial is a material that does not conduct electricity. Forhygroscopic materials that readily absorb water, such as wood, thespecific gravity differs from the density when the material moisturecontent is greater than zero. Wood density varies significantly, bothbetween and within species. In addition to the need to detect themoisture content and/or density of lumber, there exists a need to detectthe moisture content and/or density of wood particles and flakes, woodcomposite products, and other dielectric materials (such as rubber,plastics, and foods).

Detection of moisture content and/or density of wood provides a means tocharacterize wood with regard to anomalies and wood types. Detection ofknots and voids or identification of juvenile, compression, wetwood orother wood types will allow a means of sorting wood into quality orutilization classes.

SUMMARY OF THE INVENTION

The present invention, a MDD can provide a method and apparatus todetermine an unknown moisture content, density, anomaly, wood type,material type and/or other unknown characteristic of any dielectricmaterial for various purposes. Examples of dielectric materials that canbe used with the MDD include, but are not limited to, wood-basedmaterials, wood composites, agricultural and food products, plastic, andrubber.

In one embodiment, the present invention can be used to detect ananomaly and/or a wood type of a dielectric material, such as lumber.Lumber is scanned and an array of values is captured representing theattenuation and/or phase shift response of the signal to the nature ofthe wood material. This array of information provides predeterminedvalues from the dielectric material regarding the attenuation and/orphase shift signal response to variations in moisture content, density,anomaly presence or wood type. These predetermined values allowdevelopment of regression equations, threshold values or any other meansfor estimating moisture content or density differences, anomalies, woodtype, material type or other dielectric material characteristics. Forexample, Applicants have observed that phase shift decreasessignificantly when the applied signal interacts with the juvenile woodtype in green wood while attenuation changes very little. This response,if unique to juvenile wood, will allow positive identification ofjuvenile wood.

Regression equation values are values derived using a statisticaltechnique predicting the behavior of dependent variables based on knownvariables which we term herein as predetermined values. For example, inone embodiment of the invention, all possible moisture content anddensity values are recorded, and a regression equation is used topredetermine phase shift and attenuation values for all expectedmoistures and densities. The regression equation is then suitable forestimating the unknown moisture content, density values, or any othercharacteristic of the dielectric material.

Likewise, threshold values can be developed from predetermined values todetermine the expected attenuation and phase shift response for moisturecontent, anomaly, wood types, and/or other dielectric materialcharacteristics. In one embodiment the threshold values may be developedprior to scanning of the dielectric material. In a second embodiment thethreshold values may be determined during processing of the dielectricmaterial. Using lumber as an example, the relative response of signalsto moisture content, anomalies and wood type may differ if there is amoisture content difference between pieces of lumber being scanned.Therefore the threshold values for attenuation and phase shift maydiffer between each scanned piece of lumber.

Therefore, threshold values may need to be computed based onpredetermined knowledge of signal response during processing. In thisembodiment the lumber is scanned and an array of values is capturedrepresenting the attenuation and/or phase shift of the signal responsecaused by the wood types or anomalies present. The array of data isgathered and threshold values are calculated based on the relativeresponses analyzed in the light of previous knowledge (obtained frompredetermined values) as to signal reaction to anomalies and/or woodtypes. The array data is then analyzed to determine the presence ofanomalies and wood types based on the computed threshold valuescalculated from the data. While this example was based on thresholdvalues to identify anomalies or wood types, the previously describedregression or any other method of identifying anomalies based ondifferential signal response of attenuation and/or phase shift may beemployed for this purpose.

Although the MDD can be used for any dielectric material, it is veryuseful in detecting the moisture content of wood and wood-basedmaterials. In particular, the MDD can be used to detect the moisturecontent and/or density of lumber in a dry kiln prior to, during, and/orfollowing drying.

In addition, the MDD can detect the moisture content and/or density forthe purpose of assigning lumber or veneer strength grades. The MDD canalso detect moisture content and/or density of lumber, logs, poles,flakes, particles, composite panels, or any other form of solid woodproduct for any other purpose.

The MDD can also be used to monitor green wood moisture content prior toand following drying. In this case lumber, veneer, flakes, particles,etc., can be monitored and subsequently sorted on the basis of moisturecontent. Green sorting of lumber by weight is commonly done at sawmillsthat wish to maximize kiln capacity. Lumber with different moisturecontents can be dried separately allowing lumber with lower moisturecontent to be dried more rapidly. Dry sorting to detect wet wood bothbetween and within individual pieces of lumber to identify those piecesrequiring further drying is also a potential application.

In addition, the MDD can be used as a machine stress rating (MSR) deviceby which lumber strength is assessed based on density.

The above and other objects and advantages of the present invention willbecome more apparent from a reading of the following detaileddescription of the invention in conjunction with the drawings andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays an exemplary embodiment of an adjacent electroderadio-frequency device.

FIG. 2 displays an exemplary embodiment of a parallel opposed electrodedevice.

FIG. 3 displays a diagram of an exemplary embodiment of the presentinvention, a MDD.

FIG. 4 displays a diagram of another exemplary embodiment of the MDD.

FIG. 5 is a flowchart illustrating an exemplary process for determiningthe moisture content and/or density of any dielectric material.

FIG. 6 is a flowchart illustrating an exemplary process for step 525 ofFIG. 5.

FIG. 7 is a flowchart illustrating an exemplary process for step 605 ofFIG. 6.

FIG. 8 is a flowchart illustrating an exemplary process for step 615 ofFIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an apparatus and method forestimating moisture content and/or density of dielectric materials. Thepresent invention can sense the dielectric response of a radio frequencysignal or any other signal passed through the dielectric material. Aradio frequency signal or other signal can be passed between opposed oradjacent capacitance electrodes and can measure the signal strength andphase shift of the signal. The addition of phase shift and multiplefrequencies can improve the accuracy of the results of this type ofdevice for multiple layer scanning.

Although the MDD can be used for any dielectric material, it is veryuseful in detecting the moisture content and/or density of wood andwood-based materials. In particular, the MDD can be used to detect themoisture content and/or density of lumber in a dry kiln prior to, duringand/or following drying.

FIG. 1 displays an exemplary embodiment of an adjacent electroderadio-frequency device. The terms adjacent electrode and opposedelectrode denote the relative position of electrodes with respect toeach other. In an alternative embodiment, the electrodes may also becomprised of one or more adjacent pairs of electrodes or opposed andadjacent pairs of electrodes may be combined in the same device.Therefore, electrode pairs may be oriented at any angle best suited forscanning the dielectric material.

The electrodes 110 and 120 are used for transmitting and receiving theradio frequency signal or other signal 105 through the dielectricmaterial. The electrodes 110 and 120 may be of any shape and size andconstructed of any electrically conductive material. Other materials maybe incorporated into the electrodes 110 and 120. The electrodes 110 and120 may be positioned at a distance from the dielectric material surfaceor may be in direct contact. The electrodes 110 and 120 may be comprisedof brushes, rolling transducers, or be of any other type. Capacitance,and therefore signal strength, is increased as plate size and materialconductivity increases.

In one exemplary embodiment, the MDD can use an electrode shape that isrectangular and 3.0-inch by 9.0-inch in dimension. A long axis of plateis aligned with a long axis of lumber. The plates can be positioned0.250 inch from a lumber surface, but direct contact is also feasiblefor stationary wood scanning. The actual distance that the electrodes110 and 120 are positioned from the surface of the dielectric materialmay vary depending on the signal strength, frequency applied, or need ofthe specific application.

In another exemplary embodiment, the MDD can use an electrode shape ofsteel brushes applied to a wood surface. Brushes can be applied in boththe adjacent and opposed method.

In an alternate exemplary embodiment, the transmitting electrode 110 maytemporarily become a receiving electrode 120 and the receiving electrode120 can become a transmitting electrode 110. This alteration in roleswould be achieved by software or electronic switching, and would beobvious to one experienced in the art. In yet another exemplaryembodiment, the MDD can measure the moisture content and/or density ofeach face of a dielectric material. In the case of wood, for example,compression wood, wet wood, and juvenile wood all differ in moisturecontent and density from normal wood. A piece of lumber may be composedof normal wood on one face and compression wood, wet wood or juvenilewood on another. Application of adjacent electrodes on each board facewould allow comparison of differences in moisture content and/or densitybetween the two faces. This would allow determination of the presence ofthese wood types on a single lumber face.

FIG. 1 shows an adjacent electrode configuration in which bothelectrodes 110 and 120 are positioned on the same side of the woodsurface 130. A radio frequency signal or other signal generating device140 generates a radio frequency signal or other signal 105 that isapplied to the transmitting electrode 110 and sensed by the receivingelectrode 120 through an electric field 150. The radio frequency signalor other signal 105 penetrates the wood 130 on the side on which theelectrodes 110 and 120 are positioned.

FIG. 2 displays an exemplary embodiment of a parallel opposed electrodedevice. Electrodes 110 and 120 are positioned on opposite sides of thewood material 130. A radio frequency signal or other signal generatingdevice 140 generates a radio frequency signal or other signal 105 thatis applied to the transmitting electrode 110 and transmitted through thewood material 130 through the electric field 150. The radio frequencysignal or other signal 105 penetrates through the wood material from oneside to the other.

FIG. 3 displays a diagram of an exemplary embodiment of the presentinvention, a MDD. FIG. 3 displays the architecture of the presentinvention. A radio frequency signal or other signal 105 moves throughthis apparatus. The apparatus is a moisture content and/or densitydetector comprised of: a means for generating a radio frequency signalor other signal 140; one or more pairs of electrodes 110 and 120; anelectric field 150 passing through the wood material; a means formeasuring the radio frequency signal or other signal 160; and a meansfor comparing the measured radio frequency signal or other signal topredetermined values 180.

The radio frequency signal or other signal 105 can be one or multipleradio frequency signals or other signals 105. Knot presence in lumbermay increase or decrease the strength of the dielectric signal or othersignal depending on the knot characteristics relative to the clear wood.Likewise, a void in the lumber will decrease the strength of the signal.For the purpose of kiln monitoring an operator can easily avoidplacement of plates over knots or voids. For lumber sorters in whichlumber is passed at speed past electrodes a method to eliminate knotsfrom the data may be preferable. For this purpose, knot and voiddetection equipment such as a digital camera, ultrasound, x-ray, otherradio frequency device, or any other device may be employed.

The means 160 for measuring the signal strength and phase shift of theradio frequency signal or other signal 105 measures the signal strengthand phase shift caused by the interaction of the radio frequency signalor other signal 105 with the dielectric material.

The means for comparing the measured radio frequency signal or othersignal to predetermined values 180 compares the signal strength and thephase shift of the radio frequency signal or other signal 105 topredetermined values to get an estimate of the moisture content and/ordensity.

FIG. 4 illustrates a preferred embodiment of the MDD apparatus. Themeans for generating a radio frequency signal or other signal 105 is asignal generator 440. An amplifier 435 can be added to amplify the radiofrequency signal or other signal 105 generated by the signal generator440. The pair of electrodes 110 and 120 are shown with the electricfield 150. Another amplifier 435 can be added to amplify the radiofrequency signal or other signal 105 after it passes between the one ormore pairs of electrodes 110 and 120, and before it is passed to themeans for measuring the radio frequency signal or other signal 160. Themeans for measuring the signal strength and phase shift of the radiofrequency signal or other signal, or amplitude measuring and phasecomparing device 160 can be an oscilloscope 460. In this case theamplitude measuring and phase comparison is done by one device, althoughthese measurements may each be performed by separate devices. While anoscilloscope converts analog-to-digital values automatically, otherdevices may not have this feature. In this case an analog to digitalconverter is required to convert the analog signals. The means 180 forcomparing the measured radio frequency signal or other signal topredetermined values is a computer 480, which stores the signal strengthand phase shift information.

FIG. 5 is a flowchart illustrating an exemplary process for determiningthe moisture content and/or density of any dielectric material. In step505, the signal is generated by a signal generator 440 and transmittedto the amplifier 435. In step 510, the radio frequency signal or othersignal 105 is amplified by an amplifier 435 and then transmitted to theelectrodes 110 and 120. (In an exemplary embodiment the radio frequencysignal or other signal is amplified. However, the amplifier 435 andamplification step 510 may be eliminated.) In step 515, the radiofrequency signal or other signal 105 is applied to the transmittingelectrode 110, creating an electric field 150 sensed by the receivingelectrode 120.

In step 520, the radio frequency signal or other signal 105 is amplifiedby an amplifier 435 and then transmitted to the oscilloscope 460. (In anexemplary embodiment the radio frequency signal or other signal isamplified. However, the amplifier 435 and amplification step 520 may beeliminated.)

In step 525, the sensed radio frequency signal or other signal 150 fromthe receiving electrode 120 is input to the oscilloscope 460. Althoughthe oscilloscope 460 is used in an exemplary embodiment, the radiofrequency signal or other signal 105 sensed by the receiving electrodemay be analyzed for amplitude and phase shift response by any devicecapable of measuring amplitude and of comparing the phase shift causedby interaction of the wood with the radio frequency signal or othersignal. In an alternative embodiment, a spectrum analyzer, or any othercompetent device may be employed. A dedicated device with the singlefunction of comparing phase shift caused by material wood interactionwith the radio frequency signal or other signal will likely be theleast-cost solution to the phase shift measurement.

In step 530, the computer 480 stores the digitally described signalstrength and phase shift information and compares signal strength andphase shift to predetermined values to obtain estimates of moisturecontent and/or density.

FIG. 6 is a flowchart illustrating an exemplary process for step 530 ofFIG. 5. In step 605, predetermined values needed to estimate themoisture content and density are developed. While in the exemplaryembodiment provided below, the MDD used regression equations to estimatemoisture content and density, such regression equations may not berequired. Threshold values, physical constants, or any other values maybe applied to correlate predetermined signal strength and phase shiftvalues that will allow correlation of measured moisture content anddensity values to moisture content and density. Such values may beobtained by empirical observation or by theoretical analysis based onknown physical relationships of the dielectric material. In step 610,phase shift and signal strength values are measured and entered into thecomputer 480. In step 615, the measured phase shift and signal strengthvalues are compared to the predetermined values to determine themoisture content and/or density estimates.

FIG. 7 is a flowchart illustrating an exemplary process for step 605 ofFIG. 6. In step 705, relevant criteria, including phase shift and signalstrength, are measured using a known moisture content. For example, theMDD can measure the observed phase shift and signal strength values ofeach species of solid wood, the range of specific gravity values eachspecies may exhibit, and all moisture content values the wood mayexhibit. Plate material, size, shape, distance from wood surface, signalstrength and frequencies employed are made to be identical to those tobe applied by the device in practice. In step 710, regression equationmodel 1 is developed using the relevant criteria. In the example forwood, the regression equation is developed using this criteria for eachspecies of wood and for the range of moisture content. In step 715, dataand the regression equation model 1 is stored on the computer 480.

To illustrate how FIG. 7 can be applied in an exemplary embodiment, wewill use the example of how the database information is compiled for thesouthern yellow pine lumber. In step 705, green lumber is selected froma sawmill with an attempt to sample as wide a specific gravity range aspossible. Prior to drying, the green lumber is placed between theelectrodes 110 and 120 to determine the influence of the moisturecontent and specific gravity of each piece on the signal strength andphase shift of the radio frequency signal or other signal 105. Thelumber specimens are dried and periodically removed from the oven andweighed and scanned by the MDD. The periodic removals are of such alength to allow approximate reduction in moisture content of about 2percent between MDD scanning. Frequencies applied are 0.25, 0.50, 1.0,1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 MHz. Initial applied voltageis 75 volts and radio frequency amplifier output power level is 10watts. Electrode plate material is stainless steel of rectangular 3.0inch by 9.0 inch in dimension. Plate thickness is 0.0625-inch. Thelumber is to be slowly dried in an oven at 150° F.

In step 710, the regression equation Model 1 coefficients are estimatedbased on the data explained above, for the described variables of theMDD. The estimated regression equation Model 1 coefficients are employedto predict moisture content. In step 715, the resulting data andregression equation Model 1 are stored on the computer 480.

FIG. 8 is a flowchart illustrating an exemplary process for step 615 ofFIG. 6. In step 805, regression equation Model 1 coefficients are usedto calculate moisture content estimates. In step 810, a restrictedmoisture content range is identified about the moisture contentestimates. In step 815, a reduced data set corresponding to the moisturecontent values with the restricted moisture content range is segregatedfrom the total data. In step 820, a regression equation Model 2 isestimated based on the reduced data set. In step 825, the regressionequation Model 2 coefficients are used to calculate specific gravityestimates based on measured values.

The following example illustrates how FIG. 8 can be applied in anexemplary embodiment. In step 805, the entered data used regressionequation Model 1 coefficients to calculate an estimated moisture contentof 80 percent. In step 810, a reduced set of moisture content datadefined by a ±5 percent range about the 80 percent moisture contentestimate is identified. In step 815, the data corresponding to themoisture content values in the reduced data set is segregated from thetotal data set. In step 820, The R² value for the regression equationModel 2 is estimated to be 0.99. In step 825, the regression equationModel 2 coefficients are used to calculate a specific gravity estimatebased on actual measured values.

Model 1  MC=μ+F+D+D ² +PS+PS ²+ε

Where:

-   -   MC=estimated moisture content for loblolly pine lumber    -   μ=mean moisture content for loblolly pine lumber    -   F=applied frequency or frequencies (for this regression, data        for eleven frequencies were analyzed)    -   D=dielectric constant (uses signal strength measured in volts)    -   PS=phase shift    -   ε=error term

Model 2  SG _(mcr) =μ+F+D+D ² +PS+PS ²+ε

Where:

-   -   SG_(mcr)=specific gravity for loblolly pine lumber where _(mcr)        indicates a segregated data set corresponding to a restricted        moisture content range identified about the moisture content        value estimated by regression equation Model 1    -   μ=mean specific gravity for loblolly pine lumber other variables        are as previously defined in Model 1.

1. An apparatus for estimating at least one of moisture content anddensity of a dielectric material, comprising: a generator for generatinga signal in the range above 1000 MHz; at least one pair of electrodesfor transmitting and receiving said signal through said dielectricmaterial; a meter for measuring signal strength and phase shift of saidsignal caused by interaction of said dielectric material; and amicro-processor for comparing said measured signal strength and phaseshift of said signal to predetermined values to determine at least oneof moisture content and density.
 2. The apparatus of claim 1, whereinthe electrodes are adjacent electrodes.
 3. The apparatus of claim 1,wherein the electrodes are opposed electrodes.
 4. The apparatus of claim1, further comprising: at least one amplifier for amplifying saidsignal.
 5. The apparatus of claim 4, wherein the at least one amplifieris added after the generator, and before the at least one pair ofelectrodes.
 6. The apparatus of claim 4, wherein the at least oneamplifier is added after the at least one pair of electrodes, and beforethe meter.
 7. The apparatus of claim 1, wherein the meter is anoscilloscope.
 8. A method for estimating at least one of moisturecontent and density of a dielectric material, comprising; generating asignal in the range above 1000 MHz; applying said signal to at least onepair of electrodes for transmitting and receiving said signal throughsaid dielectric material; measuring signal strength and phase shift ofsaid signal caused by interaction of said dielectric material; andcomparing said measured signal strength and phase shift of said signalto predetermined values to determine at least one of moisture contentand density.
 9. The method of claim 8, further comprising: amplifyingsaid signal.
 10. The method of claim 9, wherein said signal is amplifiedafter generating said signal, and before applying said signal to the atleast one pair of electrodes.
 11. The method of claim 9, wherein saidsignal is amplified after the at least one pair of electrodes, andbefore the meter.
 12. The method of claim 8, wherein the step ofcomparing said measured signal strength and phase shift of said signalto predetermined values to determine at least one of moisture contentand density values further comprises: developing predetermined values ofsaid signal strength and phase shift for said dielectric material;measuring the signal strength and phase shift of a signal caused byinteraction of said signal with said dielectric material; and comparingsaid measured signal strength and phase shift with said predeterminedvalues to determine at least one of moisture content and density rangefor said dielectric material.
 13. The method of claim 12, wherein thestep of developing predetermined values of said signal strength andphase shift for said dielectric material comprises: measuring saidsignal strength and phase shift for said dielectric material with atleast one known moisture content and density; using a regressionequation to determine at least one unknown moisture content for saiddielectric material; and using a regression equation to determine aleast one unknown density for said dielectric material.
 14. An apparatusfor estimating at least one unknown dielectric material characteristic,comprising: a generator for generating a signal; at least one pair ofelectrodes for transmitting and receiving said signal through adielectric material; and a micro-processor for developing one or moreregression equations, comprising; a meter for measuring signal strengthand/or phase shift of said signal to develop at least one predeterminedvalue of a dielectric material characteristic based on interaction ofsaid signal with said dielectric material; and a micro-processor forusing a regression equation to determine at least one unknown dielectricmaterial characteristic based on the predetermined value of a dielectricmaterial characteristic.
 15. The apparatus of claim 14, wherein thedielectric material characteristic is at least one of: an anomaly; awood type; moisture content; density; and a material type.
 16. Theapparatus of claim 14, wherein the electrodes are adjacent electrodes.17. The apparatus of claim 14, wherein the electrodes are opposedelectrodes.
 18. The apparatus of claim 14, further comprising: at leastone amplifier for amplifying said signal.
 19. The apparatus of claim 18,wherein the at least one amplifier is added after the generator, andbefore the at least one pair of electrodes.
 20. The apparatus of claim18, wherein the at least one amplifier is added after the at least onepair of electrodes, and before the meter.
 21. The apparatus of claim 14,wherein the meter is an oscilloscope.
 22. A method for estimating atleast one unknown dielectric material characteristic, comprising:generating a signal; transmitting and receiving said signal through adielectric material; and developing at least one regression equations,comprising; measuring signal strength and/or phase shift of said signalto develop at least one predetermined value of a dielectric materialcharacteristic based on interaction of said signal with said dielectricmaterial; and a micro-processor for using a regression equation todetermine at least one unknown dielectric material characteristic basedon the predetermined value of a dielectric material characteristic. 23.The apparatus of claim 22, wherein the dielectric materialcharacteristic is at least one of: an anomaly; a wood type; moisturecontent; density; and a material type.
 24. The method of claim 22,further comprising: amplifying said signal.
 25. The method of claim 24,wherein said signal is amplified after generating said signal, andbefore applying said signal to the at least one pair of electrodes. 26.The method of claim 24, wherein said signal is amplified after the atleast one pair of electrodes, and before the meter.
 27. The apparatus ofclaim 14, wherein the dielectric material is at least one of: wood; awood-based material; a wood composite material; an agricultural product;a food product; plastic; and rubber.
 28. The method of claim 22, whereinthe dielectric material is at least one of: wood; a wood-based material;a wood composite material; an agricultural product; a food product;plastic; and rubber.
 29. An apparatus for detecting at least one unknowndielectric material characteristic, comprising: a generator forgenerating a signal; at least one pair of electrodes for transmittingand receiving said signal through a dielectric material; a meter formeasuring signal strength and phase shift of said signal caused byinteraction of said signal with said dielectric material; amicro-processor for comparing said measured signal strength and phaseshift of said signal to at least one threshold value of a knowndielectric material characteristic to determine the unknown dielectricmaterial characteristic.
 30. The apparatus of claim 29, wherein thedielectric material characteristic is at least one of: an anomaly; awood type; moisture content wood density; and a material type.
 31. Theapparatus of claim 29, wherein the electrodes are adjacent electrodes.32. The apparatus of claim 29, wherein the electrodes are opposedelectrodes.
 33. The apparatus of claim 29, further comprising: at leastone amplifier for amplifying said signal.
 34. The apparatus of claim 29,wherein the at least one amplifier is added after the generator, andbefore the at least one pair of electrodes.
 35. The apparatus of claim33, wherein the at least one amplifier is added after the at least onepair of electrodes, and before the meter.
 36. The apparatus of claim 29,wherein the meter is an oscilloscope.
 37. A method for detecting atleast one unknown dielectric material characteristic, comprising;generating a signal; applying said signal to at least one pair ofelectrodes for transmitting and receiving said signal through saiddielectric material; measuring signal strength and phase shift caused byinteraction of said signal with said dielectric material; and comparingsaid measured signal strength and phase shift to at least one thresholdvalue of measured signal strength and phase shift of a known dielectricmaterial characteristic to determine the unknown dielectric materialcharacteristic.
 38. The apparatus of claim 37, wherein the dielectricmaterial characteristic is at least one of: an anomaly; a wood type;moisture content; density; and a material type.
 39. The method of claim37, further comprising: amplifying said signal.
 40. The method of claim39, wherein said signal is amplified after generating said signal, andbefore applying said signal to the at least one pair of electrodes. 41.The method of claim 39, wherein said signal is amplified after the atleast one pair of electrodes, and before the meter.
 42. The method ofclaim 39, wherein the step of comparing said measured signal strengthand phase shift to at least one threshold value of measured signalstrength and phase shift of a known dielectric material characteristicto determine the unknown dielectric material characteristic furthercomprises: developing threshold values of said signal strength and phaseshift for said dielectric material; measuring signal strength and phaseshift of a signal caused by interaction of said signal with saiddielectric material; and comparing said measured signal strength andphase shift with said threshold values to determine the unknowndielectric material characteristic.
 43. An apparatus for determining atleast one dielectric material characteristic, comprising: a generatorfor generating a signal; at least one pair of electrodes fortransmitting and receiving said signal through said dielectric material;a meter for measuring signal strength and phase shift caused byinteraction of said signal with said dielectric material; and amicro-processor for developing threshold values of said signal strengthand phase shift for said dielectric material, comprising; a meter formeasuring signal strength and phase shift of said signal caused byinteraction of said signal with said dielectric material using at leastone known moisture content and density; a micro-processor fordetermining at least one unknown moisture content for said dielectricmaterial; and a micro-processor for determining at least one unknowndensity for said dielectric material; a micro-processor for comparingsaid measured signal strength and phase shift to said threshold valuesto determine the unknown dielectric material characteristic.
 44. Theapparatus of claim 43, wherein the dielectric material characteristic isat least one of: an anomaly; a wood type; moisture content; density; anda material type.
 45. The apparatus of claim 43, wherein the electrodesare adjacent electrodes.
 46. The apparatus of claim 43, wherein theelectrodes are opposed electrodes.
 47. The apparatus of claim 43,further comprising: at least one amplifier for amplifying said signal.48. The apparatus of claim 47, wherein the at least one amplifier isadded after the generator, and before the at least one pair ofelectrodes.
 49. The apparatus of claim 47, wherein the at least oneamplifier is added after the at least one pair of electrodes, and beforethe meter.
 50. The apparatus of claim 43, wherein the meter is anoscilloscope.
 51. A method for determining at least one dielectricmaterial characteristic, comprising: generating a signal; transmittingand receiving said signal through said dielectric material; measuringsignal strength and phase shift caused by interaction of said signalwith said dielectric material; and developing threshold values of saidsignal strength and phase shift for said dielectric material,comprising; measuring signal strength and phase shift of said signalcaused by interaction of said signal with said dielectric material usingat least one known moisture content and density; determining at leastone unknown moisture content for said dielectric material; anddetermining at least one unknown density for said dielectric material;comparing said measured signal strength and phase shift to saidthreshold values to determine the unknown dielectric materialcharacteristic.
 52. The method of claim 51, wherein the dielectricmaterial characteristic is at least one of: an anomaly; a wood type;moisture content; density; and a material type.
 53. The method of claim51, further comprising: amplifying said signal.
 54. The method of claim53, wherein said signal is amplified after generating said signal, andbefore applying said signal to the at least one pair of electrodes. 55.The method of claim 53, wherein said signal is amplified after the atleast one pair of electrodes, and before the meter.
 56. The apparatus ofclaim 43, wherein the dielectric material is at least one of: wood; awood-based material; a wood composite material; an agricultural product;a food product; plastic; and rubber.
 57. The method of claim 51, whereinthe dielectric material is at least one of: wood; a wood-based material;a wood composite material; an agricultural product; a food product;plastic; and rubber.
 58. The method of claim 14, wherein the signal is asinusoidal signal.